I should clarify that we didn't just get this engineering sample. What's possible is that the "Arctic Silver Ceramique" that Danger Den includes with the water blocks is not really Ceramique at all. If it's an inferior compound, then what I've been using is gelling at sub-zero temperatures. This is very possible, and I didn't have anything else handy at the time.

I'm not a big fan of the Ceramique. I found it extremely had to spread and it took a long time to break itself in and make good contact.